Add an Opus decoder

[tomaka]

[ishitatsuyuki]

libopus looks like BSD. Please consider using the C bindings.

[jcgruenhage]

there is someone trying to implement opus in pure rust: est31/werk

[teknico]

Another possibility is using the duckerman/magnum-opus safe bindings.

[Beiri22]

Are there any news regarding opus support?

[vlyr]

Would have use for it too.

[aprilthepink]

I think we need a contributor to tell us what would be a good way to add it to the library so we can work on doing it.

[schneiderfelipe]

Maybe relevant: SpaceManiac/opus-rs#20

[yara-blue]

I think we need a contributor to tell us what would be a good way to add it to the library so we can work on doing it.

we now have a contributors guide, see: https://github.com/RustAudio/rodio/blob/master/CONTRIBUTING.md#implementing-a-new-decoder if anyone wants to work on this we will be happy to help out.